1. Field of the Invention
The present invention relates generally to a height regulation system for an automotive vehicle for regulating the height of a vehicle body to provide an appropriate height for the vehicle. More specifically, the invention relates to a height regulation system, which limits the variation range of fluid pressure which is active for height adjustment to a predetermined pressure range so as to avoid the fluid pressure being excessively high or low.
2. Description of the Background Art
In general, a vehicular height regulation system adjusts the height of a vehicular body so that the vehicular body height can be maintained within a predetermined height range. The height regulation system includes a fluid actuator having a working chamber, in which fluid pressure is adjusted in order to adjust the relative distance between a vehicular wheel and the vehicular body. A height sensor is provided for monitoring the relative distance between the vehicular wheel and the vehicular body so as to detect the relative distance beyond a predetermined range. When the height sensor detects the relative distance between the vehicular wheel and the vehicular body being beyond the predetermined range, height adjustment is initiated to adjust the fluid pressure in the fluid actuator so that the relative distance can be adjusted within a predetermined height range.
In such a height regulation system, when the vehicular body is raised for maintenance, repair or for other causes, by means of a jack or so forth, height adjustment should be effective. However, if the height regulation system is maintained in an active state, a continous height adjustment command will be output for reducing the relative distance between the vehicular wheel and the vehicular body. As a result, the fluid pressure in the working chamber can become excessively low. Therefore, when the vehicle is returned to the ground and released from the lifting tool, e.g. jack, the vehicular height becomes so excessively low as to require height adjustment to increase the relative distance between the vehicular wheel and the vehicular body.
In the prior art, there is a proposal to disable the height adjustment when the vehicular height, i.e. relative distance between the vehicular wheel and the vehicular body, is maintained even after a height adjustment operation for a predetermined period of time. This proposal is found in Japanese Utility Model First (unexamined) Publication (Jikkai) Showa 61-10219.
Such a prior art proposal may be effective in a certain respect to avoid height adjustment operation while height adjustment a not be in effect. However, a drawback may be encountered by a delay of judgement for the ineffective state of the height adjustment. Namely, in the proposed system, judgement that the height adjustment is not effective can be made only after a height adjustment operation for a predetermined period of time. Namely, during the predetermined period of time, in which the height adjustment is active, the fluid pressure in the working chamber of the fluid actuator can be varied excessively to cause the vehicular height to be beyound the predetermined height range when the vehicle returns to the normal state.